vault backup: 2025-05-05 20:41:16

Operating Systems/Input Output.md

@@ -86,3 +86,40 @@ An alternative mode is to have the device controller send the word to DMA contro
 
 ![](Pasted%20image%2020250505195901.png)
 
+
+![](Pasted%20image%2020250505200028.png)
+
+
+### Handling interrupts
+- Microprogram or hardware checked to see if there was an interrupt pending.
+- Instruction cycle:
+	- Fethc
+	- Decode
+	- Read operands
+	- Execute
+	- Store 
+	- Check for interrupts
+
+This can be pipelined
+
+### Precise interrupts
+1. PC is saved in a known place
+2. All instructions before the one pointed to by the PC have completed
+3. No instruction beyond the current one has vfinished
+4. Execution state is known
+
+An interrupt that doesn't meet the above requirements is called **imprecise**
+
+![](Pasted%20image%2020250505200548.png)
+
+## Clocks
+![](Pasted%20image%2020250505201102.png)
+
+> [!IMPORTANT]
+> Watchdog timers **ARE clocks**
+
+
+
+## Mass Storage
+Secondary storage for modern computers and shit.
+

Operating Systems/Mass Storage.md

@@ -0,0 +1,38 @@
+
+## Hard disks (HDDs)
+Spin platters of magnetically-coated material under moving RW heads
+- Rotate at 60 to 250 times/s
+- Transfer rate is rate at which data flows between drive and pc
+- Positioning time (Random access time) to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency)
+
+![](Pasted%20image%2020250505201859.png)
+
+
+### Controller
+Receives data/ command from the OS, controls I/O operation and sends back results to OS
+![](Pasted%20image%2020250505201950.png)
+
+
+### I/O steps
+- Move head to track -> Seek Time (S)
+- Find sector -> Rotational Latency Time (r)
+- Transfer data to/from controller -> Block Transfer Time (btt)
+- Error checking and report to OS
+
+
+### Disk Formatting
+Each platter must receive a low-level format done by software, i.e. marking the cylinders and tracks, each containing a few sectors, with short gaps in between
+
+Each sector includes:
+- Preamble: starts with start of the sector bit pattern, the cylinder and sector numbers
+- Data: size of the data portion is determined by the formatting program -> 512 bytes usually
+- ECC: error correction, typically 16 bytes
+
+
+Numbering the sectors
+- Position of sector 0 on each track is offset from the previous track when the low-level format is laid down (cylinder skew)
+
+
+![](Pasted%20image%2020250505202532.png)
+
+![](Pasted%20image%2020250505203114.png)