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Terminals
- Connect to computers via serial lines (RS-232) : 9600 baud (bits/sec)
900 bytes/sec
- Although small rate of transfer - can swamp CPU die to overhead of handling each byte
- Say 10 users (running vi or emacs) = 900 interrupts per user : overhead of handling interrupt
100 microseconds
- Direct Memory Access : Instead of interrupt on every block - do a block transfer - then
interrupt (overall - faster transfer rates)
- Redirection : Bitmap displays : CPU writes to video memory - display then reads video
memory
Disks
- Options : choice of sector size (tradeoff between space and time efficiency), usually
big blocks mean greater transfer rate (time efficiency) as time to find data on disk is minimised
Trends in Disk Technology
for a typical disk today :
- Disk capacity : 2.1 GB
- Number of surfaces per pack : 18
- Number of tracks per surface : 2048
- Number of sectors per track : 32
- Number of bytes per sector : 1 KB
- Number of revolutions per minute : 7200
Transfer rate = 1 KB bytes/sector * 32 sectors/cycle * 120 cycles/second = 4 MB/sec
Omer F Rana
Fri Feb 14 18:33:29 GMT 1997