diff --git a/content/notes/23-IO-systems.md b/content/notes/23-IO-systems.md
index 13c785337..9870e01ad 100644
--- a/content/notes/23-IO-systems.md
+++ b/content/notes/23-IO-systems.md
@@ -4,6 +4,9 @@ aliases:
 tags: 
 - cosc204
 - lecture
+sr-due: 2022-11-04
+sr-interval: 3
+sr-ease: 250
 ---
 
 interactive between device drivers and IO devices
@@ -49,8 +52,15 @@ Direct memory access
 
 IO performance
 - reduce context switches
-- reduce data copies in memory (normamly two: user mem)
+- reduce data copies in memory (normamly two: user memory, device/kernel memory): can mmap to share memory
 - reduce number of interrupts (e.g., using polling)
+	- it data is coming more frequently polling may be faster than interrupts
 - increase concurrency (e.g., DMA)
 - move data processing to hardware (e.g., network interface card)
-- balance CPU, memory system, bus, IO performance
\ No newline at end of file
+- balance CPU, memory system, bus, IO performance
+
+Zero-copy
+- avoid memory copy in IO data transfer
+- use dynamic mmap
+- copy data from deice directly to user spce e.g., remote direct memory access RDMA
+- pass packet buffer pointers between layers of TCP/IP protocol
\ No newline at end of file
diff --git a/content/notes/cosc-204.md b/content/notes/cosc-204.md
index 1e0c06b5b..3ac05f63a 100644
--- a/content/notes/cosc-204.md
+++ b/content/notes/cosc-204.md
@@ -53,7 +53,7 @@ tags:
 - [20-sync-deadlock](notes/20-sync-deadlock.md)
 - [21-memory-management](notes/21-memory-management.md)
 - [22-virtual-memory](notes/22-virtual-memory.md)
-
+-[23-IO-systems](notes/23-IO-systems.md)
 
 # Archive