Looking for 1Mx8 EPROMs (27C080 or 27C801) Al Kossow aek at bitsavers.org <mailto:cctalk%40classiccmp.org?Subject=Looking%20for%201Mx8%20EPROMs%20%282 7C080%20or%2027C801%29&In-Reply-To=> Sat Jun 7 16:15:04 CDT 2008 * Previous message: Looking for 1Mx8 EPROMs (27C080 or 27C801) * Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] ________________________________ How much of the megabyte of space have you ACTUALLY used? A meg of EPROM seems insane to me for a low-cost SBC. ________________________________ * Previous message: Looking for 1Mx8 EPROMs (27C080 or 27C801) * Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] ________________________________ More information about the cctalk mailing list <http://www.classiccmp.org/mailman/listinfo/cctalk> -----REPLY----- Hi Al, Insane is such a harsh word... :-) I consider it a slight modern adaptation to a Z80 SBC designed in the classic vintage style. Of the 1MB EPROM, the current SBC uses a little over 128K. It includes the boot loader, RAM monitor, CP/M boot image, the standard transient CP/M commands, the VDE full screen editor, BBC basic, and a smattering of small utilities like the RTC, XMODEM5, and start-the-RAM-monitor-from-CP/M. The rest of the EPROM is reserved for user expansion in the various CP/M USER spaces. The SBC really only needs probably 4K or so to boot the RAM monitor but the rest of the ROM is used as CP/M block devices (32K A: and 992K F: drives). There is also a 448K RAM block device for CP/M drive B: for temporary files in addition to the full 64K main memory for the OS and RAM monitor. Memory block devices allow the SBC to have a usable and reliable OS for relatively easy user expansion without the hassle and reliability issues of real disk devices. Real disk drives are supported (IDE and floppy) on a Disk IO board I built on the prototype. I plan to make a PCB for later on. Disks are good things but I made them an option rather than a requirement to keep it simple. Believe me, a 1MB EPROM block device is *MUCH* less expensive than adding even the least expensive floppy drive controller and even IDE. The ROM control circuitry is there regardless of size and the cost difference between a 27C64 and a 27C801 is minimal in the overall cost. The benefits of reliable storage tremendously outweighs the minor extra cost, IMO. Thanks and have a nice day! Andrew Lynch