Project ForgeConsider a storage disk with 4 platters, 200 cylinders (0-199), and 256 sectors per track. 6 disk requests [sector, cylinder, platter] arrive simultaneously: [120,72,2], [180,134,1], [60,20,0], [212,86,3], [56,116,2], [118,16,1]. The head is at cylinder 80, moving towards higher cylinder numbers. Average power dissipation moving the head over 100 cylinders is 20 mW; reversing direction once costs 15 mW; rotational latency and platter-switch power are negligible. Using Shortest Seek Time First (SSTF), the total power consumption in milliwatts is ____.
Explanation
Requested cylinders: {72,134,20,86,116,16}. SSTF trace from 80: →86(dist6,up)→72(dist14,DOWN,reversal)→116(dist44,UP,reversal)→134(dist18,up,same)→20(dist114,DOWN,reversal)→16(dist4,down,same). Total seek distance = 6+14+44+18+114+4 = 200 cylinders → 200/100×20 = 40mW. Direction reversals: 3 (up→down, down→up, up→down) → 3×15 = 45mW. Total = 40+45 = 85mW.
Source: GATE CS 2018 (2018)
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