Media Recognition - Floppy Disks part 2

3 inch Disks

Type:	Magnetic storage media
Introduced:	1973
Active:	Only by existing users.
Cessation:	Never reached huge popularity due to dominance of 3.5” disks and then declined in 1990s. Amstrad computers, which included a 3” drive, stopped being produced in the late 1990s
Capacity:	Either 180, 360 or 720KB
Compatibility:	Only a few machines have inbuilt 3” drives. These are the Tatung Einstein, Sega SF-7000, Osborne and several Amstrad models including the ZX Spectrum +3, PCW 8512, 8256, 9512, CPC 6128.
Users:	A limited number of individual users and small organisations. Used for data storage and backup.
File Systems:	CP/M
Common Manufacturers:	Disks: Amsoft, Maxell, Matsushita, Tatung Drives: Maxell, Hitatchi, Matsushita

Recognition

These disks are double sided, but with each side remaining independent. This means that single-sided disk drives can still read both sides by flipping the disk. Because the two sides are independent of each other they are labelled either ‘A’ and ‘B’, or ‘1’ and ‘2’ to help distinguish between them. Each side also had a dedicated write-protect hole, which may be implemented differently from manufacturer to manufacturer.

3” disks are commonly labelled either CF2 (single density) or CF2DD (double density). However, if a disk has no label the density can be determined using the CP/M programme called ‘Disckit’

High Level Formatting

The CP/M operating system was used by Amstrad and other computers with 3 inch disk drives, hence 3 inch disks most commonly contain the CP/M file system.

3 Inch Disk Drives

3” disk drives were most common on Amstrad computers. The first model, the PCW 8256 had one single sided drive. The later model, PCW 8512, had two drives placed one on top of the other to the right of the monitor screen. The upper drive remained single sided, whereas the lower was double sided and double density. The ZX Spectrum +3 also used the same SS drive as the Amstrad 8256.

5.25 Inch Disks

Type:	Magnetic storage media
Introduced:	1976
Active:	Only by existing users with 1980s legacy machines
Cessation:	Largely superseded by 3.5” floppies by the start of the 1990s. Windows 95 came with no 5.25” floppy drive.
Capacity:	110 – 1,200 KB
Compatibility:	Contemporary machines had inbuilt 5.25” floppy drives. Drives can be externally attached to modern computers. Compatibility issues with MFM drives and GCR encoded disks and vice versa.
Users:	Almost universal during the height of their popularity in the 1980s. Used by individuals and small individuals for data storage and backup and by manufacturers for booting software.
File System:	CP/M, FAT, Apple DOS File System, DFS
Common Manufactures:	Disks: IBM, Maxell, Apple, Verbatim, BASF, Drives: Shugart Associates, IBM, Apple, Tandon

Recognition

5.25” disks are physically very similar to 8 inch disks, just at a reduced scale.

The only way to visually distinguish between SS and DS 5.25” disks is by reading the labels, if there are any. However, users realised they could extend the capacity of a single sided disk by cutting a second write-enabled slot and index hole into the plastic cover. By flipping the disk over and inserting the disk this way a user could use the other side of the disk. These were known as ‘flippy disks’ and any disk adapted in this way can be identified as a manufactured single sided disk customised to become double sided. Users can also customise disks to make them read-only by covering the write-enabled slot (on the top right side in the image) with tape such as masking tape.

Reading the label is also the only way to visually distinguish between HD and DD disks. If nothing is written on the disk, the possible disk types can be narrowed down if the creation date is known. This is not always a very accurate method, but if a disk pre-dates the introduction of a format this can help identify it. For example, HD disks were not available until 1984, therefore a disk from 1980 cannot be HD.

• 1976 = First 5.25" floppy developed
• 1978 = Apple introduce a 5.25" floppy for Apple II
• 1978 = DD 5.25" floppies introduced
• from 1978 = People begin making 'flippy' disks
• 1984 = HD 5.25" flopies introdced
  

The other option is to identify the density based on the disk capacity. This is easily achieved with Windows operating systems. Connect the 5.25” floppy disk drive to a computer running Windows and insert the floppy disk. Open the file manager, right click on the floppy drive icon and select properties. A new window will open which states the disk capacity as well as the amount so far used by the disk.

High Level Formatting

There are various possible file formats that are compatible with 5.25” floppy disks, though compatibility depends on the low level format of a disk and the computer drive it is intended for.

CP/M: Found on some 5.25” disks intended for use with CP/M operating system. As MS-DOS gained popularity it supplanted CP/M, which then rapidly declined from 1981.

File Allocation Table 12 (FAT12): FAT was, until 2000, the file system of choice for MS-DOS and Microsoft Windows. FAT12, the first FAT version introduced in 1977, was designed specifically for floppy disks and replaced CP/M as the most common file system found on floppy disks, particularly FM and MFM encoded ones.

Apple DOS File System: In 1978 Apple introduced Apple DOS File System, their own system designed for Apple computers and floppy disks and hence only compatible with Apple operating systems.

Disc Filing System (DFS): Designed in 1982 by Acorn Computers Inc. for their 5.25” floppy disk drives. This uses FM encoding, therefore only produces single density disks. A double density disk can be formatted to use DFS, but this would render it single density.

5.25” Disk Drives

Early 5.25” drives could only read one side, regardless of what type of disk was inserted and double sided drives were not available until 1978.

Disk II was the first floppy disk drive to be used by Apple for their Apple II microcomputers. This drive was single sided, but supported flippy disks. In 1984 the Apple IIc was the first to include a built in floppy drive, the Disk IIc.

The first Commodore 5.25” disk drive was the Commodore 1540, though more common was the Commodore 1541, a single sided 170KB GCR drive. Several subsequent versions were manufactured which were double sided and could read and write both GCR and MFM encoded disks.

Computers running PC-DOS and MS-DOS were slower to incorporate 5.25” disk drives, the first not being included until 1981 and that was only a single sided drive. Double sided floppy disk drives were included from 1982 onwards with the release of version 1.1 of MS-DOS.

3.5 Inch Disks

Type:	Magnetic storage media
Introduced:	1982
Active:	Still used by some for data backup, storage and transport. Compatible floppy disk drives are no longer a common feature in standard PCs.
Cessation:	Use declined in the late 1990s as optical storage media became more popular. From 1998 manufacturers began to produce computers without inbuilt floppy drives, though they are still in use by people with older machines.
Capacity:	360 – 2,880 KB
Compatibility:	Twentieth century PCs with inbuilt 3.5” floppy drives; and newer PCs with USB ports may use an external USB 3.5” floppy drive.
Users:	Almost universal use during 1980s and 90s by individuals and small and medium organisations.
File Systems:	FAT, NTFS, DFS, ADFS, Apple DOS File System, MFS, HFS
Common Manufacturers:	Disks: Many manufacturers and brands including Sony, Apple, Olivetti, Golding, Drives: Many manufacturers including Sony, Apple, Dell

Recognition

The first 3.5” disks were SS, but DS disks quickly became the standard after being introduced. Aside from it being stated on the label there is no visual way to determine which a disk is.

Some disks state the density on the disks themselves, either writing the words or using acronyms. If nothing is written there can still be clues to help distinguish the disk type. For instance, after the introduction of HD it became possible to format DD disks to HD by cutting or punching a hole in the bottom right hand corner. Special square hole-punchers were available for this purpose and disks would include a square indent where the hole should be, as can be seen in the image below:

High density disks have ‘HD’ displayed on the top right corner and have a hole in the bottom right corner rather than an indent. Taping over or covering up the hole reduces an HD disk to DD. The point of the hole is to help the disk drive determine the density. Extended Density disks have a second square hole opposite the high density hole.

High Level Formatting

As floppy disk production developed, so did the range of file systems available. Therefore, there are more possible file systems to be found on 3.5” floppy disks

Apple DOS File System: Apple II’s UniDisk 3.5 Drive used this file system, but the drive was never very popular and was soon discontinued.

Macintosh File System (MFS): Created by Apple Inc. and introduced along with their Macintosh 128K computer in 1984. It can be used with Apple’s 400K 3.5” disks, but cannot support the 800K disks. From the Mac OS 8.1 onwards (1998) Apple computers were no longer able to use MFS.

Hierarchical File System (HFS): Developed by Apple in 1985 as a revised version of MFS. An an improved version, HFS+ was introduced in 1988. Like MFS, HFS is only compatible with Macintosh operating systems.

DFS: Early Acorn 3.5” disks were formatted to use DFS, but this was later replaced with Advanced DFS.

Advanced DFS (ADFS): ADFS, introduced in 1983, uses MFM encoding and so supports Acorn’s double density 3.5” floppy disks up to 640KB in size. However, ADFS cannot support high density disks and ADFS formatted drives are not compatible with DFS disks.

Extended File System (ext): ext was created in 1992 specifically for Linux systems and was replaced by ext2 in 1993.

FAT12 and FAT16: FAT12 was the file system of choice for 3.5” disks until 1987 when FAT16 was introduced.

New Technology File System (NTFS): In 1993 NTFS was introduced as the standard file system for Windows operating systems, superseding FAT by 2000.

To find out which file system is in use on a 3.5” floppy disk using Windows XP insert the disk in the floppy drive and open ‘My Computer’. From here right click on the floppy drive icon and select ‘Preferences’. This will open a screen displaying disk data including the file system.

3.5 Inch Disk Drives

Apple’s range of Macintosh computers were separate from the Apple range and had their own disk drives. The first Macintosh computer, Macintosh128K introduced in 1984, uses a 400K Macintosh External Disk Drive which is single sided. Subsequent computers use the double sided 800KB External Disk Drive. In 1985 Apple released the Apple UniDisk 3.5 drive for the Apple II. This increased capacity to 800K, but was never very popular with Apple II users as most software was still released on 5.25” disks to accommodate older Apple II machines. Despite being very similar to the Macintosh drives the two are incompatible. However, in 1986 Apple introduced the Apple 3.5” Drive, a cross-platform floppy disk drive that is compatible with both Macintosh and Apple computers. This was part of an overall strategy to unify Macintosh and Apple manufacturing.

Despite using both GCR and MFM encoding methods, the first Commodore to read 3.5” disks was the Commodore 1581, which read only MFM encoded disks.

The first IBM model to include a 3.5” drive as standard was the IBM PS/2 in 1987, though 3.5” drives could be found on later versions of the IBM AT. Initial IBM PS/2 drives only supported double density disks, but later models included support for high density disks. MS-DOS 3.2, introduced in 1986, was the first operating system to natively support 3.5” disk drives, up to double density capacity. HD support was included in MS-DOS 3.3 (1987) and ED compatibility came with MS-DOS 5 in 1991.

Media Recognition - Floppy Disks part 1

When archivists receive a collection one of the first things they’ll need to do is identify any digital material. However it won’t be enough to single out for instance all the floppy disks or the CDs – there are subtler distinctions that need to be made. Archivists might not be aware of all these distinctions (or might need reminding) so I’ve been writing a media recognition guide to help archivists determine the specific types of data storage device they may come across. I thought I’d share some of this work with you and first up we have: Floppy Disks.

Sizes

Floppy disks come in four sizes. 8” and 5.25” disks are encased in bendable plastic, 3.5” disks (which are actually 90 x 94mm) are encased in rigid plastic and have sliding metal shutters and 3” disks also come in rigid plastic which is harder than the 3.5” covering and are thicker than the other disk.

Low Level Format

Floppy disks are either single sided (SS) or double sided (DS) and this is often stated on the manufacturer’s label, if the disk has one. Being SS or DS affects a disk’s capacity, but the bigger factor is the low level format, or density of a disk. There are 5 possibilities:

Single Density (SD) - First type of floppy disk available.

Double Density (DD) - On average twice as many bits per time unit can be encoded compared to data on a single density disk, thereby doubling the capacity.

Quad Density (QD) - Holds four times as much data as a single density disk.

High Density (HD) – Further expands disk capacity allowing 5.25” disks to store up to 1,200 KB and 3.5” disks to store up to 1,440 KB of data

Extended Density (ED) – Enlarges disk capacity to 2,880 KB

Not all sizes of disk are compatible with the different densities, which is important to know when identifying the disk type.

Size and number of sides used	Possible Densities	Capacity
8 inch single sided	Single	250 KB
8 inch double sided	Single	500 KB
	Double	1.2 MB
3 inch single sided	Single	180 KB
	Double	360 KB
3 inch double sided	Single	360 KB
	Double	720 KB
5.25 inch single sided	Single	80 KB
	Single	90 KB
5.25 inch double sided	Single	180 KB
	Double	320 KB
	Double	360 KB
	Quad	720 KB
	High	1,200 KB
3.5 inch single sided	Double	360 KB
	High	720 KB
3.5 inch double sided	Double	720 KB
	High	1,440 KB
	Extended	2880 KB

Writing to Disk Methods

There are two ways in which data is written to a floppy disk. The tracks on floppy disks are smaller on the inside of the disk than on the outside, therefore when writing data the disk can either maintain a constant speed in terms of the time taken for the disk to rotate 360 degrees or in terms of the time taken to cross each track. Constant Angular Velocity (CAV) maintains a constant rotation speed whereas Constant Linear Velocity (CLV) ensures that each track is crossed at the same speed.

CAV is used by most microcomputer platforms, such as IBM PC, Amstrad CPC and Microsoft Windows, but Apple adopted CLV. This method is more efficient, thus explaining why Apple disks have larger capacities. However, CLV requires a special mechanism, which renders Apple floppy disks incompatible with other computers. Apple eventually abandoned this method and adopted the CAV standard.

8 Inch Disks

Type:	Magnetic storage media
Introduced:	1971
Active:	No
Cessation:	Quickly declined in popularity after the 5.25” disk was introduced and by 1978 most manufacturers had adopted 5.25” disk drives.
Capacity:	500 KB – 1.2 MB
Compatibility:	Contemporary machines had inbuilt floppy drives. Drives can be externally attached to modern computers.
Users:	Almost universal during the height of their popularity in the 1970s: was one of only a few affordable mass storage devices available. Used by individuals and small organisations for data storage and backup and by manufacturers for booting software.
File Systems:	CP/M most common. Also ODS-1
Common Manufacturers:	Disks: IMB, Maxell, Shugart Associates, 3M Drives: IMB, Shugart Associates, Burroughs Corporation

Recognition

The 8 inch floppy was the first disk to be introduced in 1971. Like the other disk sizes, 8 inch floppy disks consist of a disk with a central hole encased in a plastic envelope.

The easiest way to identify the low level format of an 8” floppy disk is by any labelling on the disk. The majority of manufacturers brand the disk as double density if that is what it is. The format ‘Single Sided’ was not coined until Double Sided was invented in 1976, therefore early SS disks will not be labelled as such. However, this does not mean all unspecified disks are single sided. Likewise it is difficult to determine the density of a disk if this is not labelled, although the capacity of the disk is a good indicator.

High Level Formatting

All files written to a floppy disk are contained within a file system. The specific file system used depends on the disk manufacturer, but 8” disks will generally contain either ODS-1 or CP/M

8 inch Disk Drives

The first read-write 8” floppy drives were introduced in 1972 with a capacity of 175 KB. In 1973 IBM released its own floppy disk drive which used a different recording format thereby increasing the capacity to 250 KB. This became known as Single Sided Single Density (SSSD) and drives supporting SSSD were soon being made by several manufacturers. 8” floppy disk drives were the storage device of choice used by the first ‘microcomputer’ operating system in the 1970s. Double sided drives were first introduced by Burroughs Corporation in 1975 with a 1 MB capacity.