★ HARDWARE ★ LECTEURS DE DISQUETTES ★ MEGADRIVE ★ |
| Lecteurs Externe - Megadrive (Amstrad Action) | Hardware Lecteurs De Disquettes |
Several companies are pushing 5"¼-inch second drives for the Amstrad. Many (including Silicon Systems) claim their drives harmonize perfectly With the existing operating systems Amsdos, CPM 2.2 and CPM Plus. So far none have achieved particularly good compatibility. Silicon boasts more than most. Have they resolved all the problems? Does the Megadrive deliver? Perhaps you think one disk-drive is enough. Have you ever used a CPM application program, for example, Super Calc II or New Word?. Then you'll have found that most of the disk is taken up by the program, leaving precious little space for your data. Sure you could swap disks, but that's not ergonomic or elegant, :tot to mention time-consuming. And unfortunately certain CPM programs (WordStar and its clone NewWord are culprits that spring to mind) dont like disks being swapped during a work-session - a rode crash normally results. Backing up disks with one drive is a dreary task involving much disk-swapping. A second drive makes the job faster and simpiei. A dual-drive system has its advantages {certainly no disadvantages) under Amsdos as well. When using Prospell (Protexts spoil-checker) you can place the dictionary disk in drive B and the disk with your rext file in drive A - fast and simple. And in its quiet moments dr.ve B makes a great stand for your coffee-cup. (As long as you don't wind coffee all over your drive, disks and keyboard, that is Ed.) Silicon's 5"¼ inch drive is sleek, has a colour scheme to match Arnold and a good solid feel.' As a general rule of thumb, the heavier the drive (excluding the casing and power supply of course), the better its quality. The Megadrive- plugs into the mains and into the second-drive port at the back of your 664 or 6128. If your machine is a 464, it plugs into the connector embedded in the ribbon cable. In all cases, a further interface plugs into the expansion port. This interface just happens to be a stripped-down Amram (reviewed in issue 19) add its full features for an extra £20. Along wish the drive and interface you receive software to format the 5¼ inch disks and transfer files back and forth from 3 inch to 5¼ inch. And at performs more marvellous trickery. Read When you plug in an ordinary 3 inch second drive it's immediately usable As you may have discovered when formatting or cataloguing a disk, either 169 or 178k of storage is available, depending on the format chosen. A formatted disk is divided into concentric circles known as tracks (numbered from 0 to 39); each track is subdivided into 9 equal sectors. Each track holds 4.5k. And 4.5 times 40 is 180, so each disk holds 180k of information. Both Amsdos and CPM reserve 2k for the directory. This explains the figure 178k: the data format. If you formal a disk for use with CPM, two tracks: (9k) are reserved to hold much of the CPM operating system, leaving 169k: system or vendor format. If you use the-Megadrive as it stands (without the Amram interface and software) then the same miserable amount of disk space is available, Why? Amsdos and CPM are configured to read and write to a maximum disk capacity of 178k. Furthermore, the drive mechanism used with the Amstrad 3-inch drives cannot handle more than 40 tracks and, unless told otherwise, the operating system thinks it has .only this basic, unit to play with. The Megadrive. is a different breed of drive: instead of having one drive-head to read data, it has two. One sits each side of the floppy disk The disk is inserted only one way up, and the system reads or writes both sides. Moreover, each head is capable of accessinq 80 tracks. Just think, ordinary 3-inch disks hold 1801c of information on 40 tracks. So 80 tracks and two heads should give you a staggering 4 times 180k of free space. Indeed thus is not far off the mark. After space has been reserved for CPM and the directory, the final storage capacity is 706k. With this beefed-up system. 128 directory entries are possible: 128 different files rather than the standard 64 can be kept on a single 5¼ inch floppy disk. For Amsdos or CPM to make use of Megadrive's capabilities, a mixture of software and hardware is required. These come in the form of Amram and Megadrive Software. At the start of day. all you need to do is run the software. This copies the number-7 ROM (disk rom) into Amram's 16k ram, patching it en route. Amram now acts as the disk rom, and all the capabilities of the Megadrive are yours. CPM 2.2, once it too is altered by running a patch file, will accept The Megadrive and all its storage capacity. One disadvantage is that the interface uses up ROM socket 5. moving Amsdos even lower down into user memory. As a result, large programs sitting high in memory might not run. Adding a second drive may not come top of your priorities list. But as it's a 5¼-inch drive, fully compatible with Amsdos and CPM and can store over 700k of data (more than two entire issues of AA) on each disk, then now may be the time to think again. The Megadrive is most certainly a well thought out product it delivers!
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