L17io - CS324: Computer Architecture CS324: Computer...

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S324: Computer Architecture CS324: Computer Architecture Lecture 20: Busses & I/O
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Motivation for Input/Output ± I/O is how humans interact with computers O gives computers long rm memory ± I/O gives computers long-term memory. ± I/O lets computers do amazing things: – Read pressure of synthetic hand and control synthetic arm and hand of fireman – Control propellers, fins, communicate in BOB (Breathable Observable Bubble) ± Computer without I/O like a car without wheels; great technology, but won’t get you anywhere
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I/O Device Examples and Speeds ± I/O Speed: bytes transferred per second (from mouse to Gigabit LAN: 7 orders of mag!) evice ehavior artner ata Rate ± Device Behavior Partner Data Rate (KBytes/s) Keyboard Input Human 0.01 ouse put uman 02 MouseInput Human 0.02 Voice output Output Human 5.00 Floppy disk Storage Machine 50.00 P i t t t 00 00 Laser Printer Output Human 100.00 Magnetic Disk Storage Machine 10,000.00 Wireless Network I or O Machine 10,000.00 Graphics Display Output Human 30,000.00 Wired LAN Network I or O Machine 125,000.00 When discussing transfer rates, use 10 x
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What do we need to make I/O work? APIs Files ± A way to connect many types of devices to the Proc-Mem Operating System roc em ± A way to control these devices, t t t h t Proc Mem CI Bus respond to them, and transfer data ± A way to present them to user programs so they are useful PCI Bus CSI Bus SCSI Bus cmd reg. data reg.
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Magnetic Disk Regi s C a M rpose: ters che emory Disk ± Purpose: –Long term, nonvolatile storage arge inexpensive but slow –Large, inexpensive, but slow –Lowest level in the memory hierarchy ± Characteristics: ely on a rotating platter coated with a magnetic surface Rely on a rotating platter coated with a magnetic surface –Use a moveable read/write head to access the disk
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Organization of a Hard Magnetic Disk latters Platters Track ± Typical numbers (depending on the disk size): –10,000 to 50,000 tracks per surface Sector ,, p – 100 to 500 sectors (smallest unit that can be read or written) per track ± Originally, all tracks had the same number of sectors: gy , – Constant bit density: record more sectors on the outer tracks ± Now: constant spacing b/w bits, speed varies with track location
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Magnetic Disk Characteristics Sector Track Cylinder latter ± Cylinder: all the tracks under the head at a given point on l surfaces Head Platter all surfaces ± Read/write data is a 4-stage process: –Seek time: position the arm over the proper track –Rotational latency: wait for the desired sector to rotate under the read/write head –Transfer time: transfer a block of bits (sector) under the read- write head –Disk controller time: overhead to transfer from disk to memory
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Magnetic Disk Characteristics ector Track Sector ylinder k t i t d b t h i d t Cylinder Head Platter ± Average seek time as reported by the industry: –Typically in the range of 3 ms to 13 ms um of the time for all possible seek) / (total # of possible –(Sum of the time for all possible seek) / (total # of possible seeks) ± Due to locality of disk reference, actual average seek time may: –Only be 25% to 33% of the advertised number
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L17io - CS324: Computer Architecture CS324: Computer...

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